Electrostatic Clutch and Transmissions

ABSTRACT

Methods and apparatus related to electrolaminate clutches and transmissions are disclosed. A device can include: an input shaft that can be coupled to an electrolaminate sheet; an output shaft that can be coupled rigidly to a spring positioned over the input shaft, where the spring includes a tab that fits a groove of a spring capture ring that can be positioned over the input shaft; and a drum connected to an electrical ground between the electrolaminate sheet and the spring capture ring, where the drum can be coupled rigidly to the spring capture ring. Then, when a voltage is applied to the electrolaminate sheet, the electrolaminate sheet can clamp to the drum and impart rotation of the input shaft to the drum. The imparted rotation can cause the spring capture ring and the spring to rotate and clamp down on the input shaft, imparting rotation to the output shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/219,263, filed Jul. 25, 2016, which claims priority to U.S. PatentApplication No. 62/196,182, filed Jul. 23, 2015. The foregoingapplications are incorporated herein by reference.

GOVERNMENT LICENSE RIGHTS

This invention was made in part with Government support under contractnumber W91CRB-10-C-0139 awarded by the U.S. Army. The Government hascertain rights in this invention.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Robots are currently being used in numerous applications and in numerousways. A few examples of their utilization may be found in industrialapplications where robots are used to perform repetitious or strenuoustasks and in medical applications sometimes to assist a surgeon toperform surgery. For all their proliferation, robots are still limitedin various ways. One limitation which characterizes many robots is thatthey can only operate for a certain amount of time with a given batterysize. One cause of this limitation is due to the losses that occur inthe process of converting electrical energy to mechanical outputs.Improving the efficiency of conversion would then directly lead tolonger operation time given a battery size. In addition, the concepts toimprove efficiency in mobile robots may be advantageous on stationarywall-powered robots as well. For example, improved efficiency may leadto smaller motors thus leading to more compact design. Yet anotherlimitation that also characterizes many robots is that they are oftendesigned for the worst case load and speed conditions, making them bigand bulky. This is because a robot designer generally picks a settransmission ratio for each actuator. Currently available variabletransmissions, such as the nuVinci or belt-driven conical continuouslyvariable transmissions used in larger vehicles, are generally lessefficient and much heavier and bulkier than single-speed optionsavailable to robot designers. Theoretically, smaller motors or actuatorscould be used if variable transmissions were comparable in efficiency,size, and weight. Designing a robot that can quickly adapt to changingload conditions and operate with high efficiency would be desirable.

SUMMARY

Some embodiments of the present disclosure provide a method. The methodincludes coupling an input stage to an output stage utilizing twosurfaces. At least one of the surfaces is flexible and thin. The twosurfaces are electrostatically clamped together when a voltage isapplied across the two surfaces. When the two surfaces are clamped, aninput rotation is imparted to rotate the output stage. When the voltageis not applied, the input rotation is not imparted to the output stage.

Some embodiments of the present disclosure provide a two speedtransmission system. The two speed transmission system includes a firstand second electrolaminate disc clutch, where the first disc clutch isassociated with one or more gear stages, and where the second clutch isassociated with an output stage.

Some embodiments of the present disclosure provide a device. The deviceincludes comprising: an input shaft coupled to an electrolaminate sheet,an output shaft coupled rigidly to a spring positioned over the inputshaft, the spring having a tab that fits in a groove within a springcapture ring, the spring capture ring positioned over the input shaft, adrum connected to an electrical ground positioned between theelectrolaminate sheet and the spring capture ring, where the drum iscoupled rigidly to the spring capture ring. The electrolaminate sheet,when a voltage is applied to the electrolaminate sheet, clamps to thedrum and imparts rotation of the input shaft to the drum causing thespring capture ring to rotate, which subsequently causes the spring torotate and clamp down on the input shaft to impart rotation to theoutput shaft.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates one surface of an electrolaminate clutch.

FIG. 1B shows a configuration of a clutch using two flexible surfaces.

FIG. 1C shows a configuration of a clutch using one flexible surface andone metal surface.

FIGS. 2A-B illustrate an electrolaminate disc clutch.

FIG. 2C illustrates a detailed implementation of the electrolaminatedisc clutch.

FIG. 2D illustrates the cross-sectional view along section AA shown inFIG. 2B.

FIGS. 2E, 2F, and 2G illustrate three other configurations of the discclutch design.

FIG. 2H illustrates a perspective exploded view of the clutch.

FIGS. 2I and 2J illustrate how to calculate the maximum torque transfer.

FIG. 2K illustrates a construction of clutch surfaces.

FIGS. 3A, 3B, 3C, and 3D illustrate a two speed gear box usingelectrolaminate clutches.

FIGS. 4A. 4B, and 4C illustrate an electrolaminate band clutch

FIGS. 5A and 5B illustrate a wrap spring clutch.

FIG. 6A illustrates an exploded view of device using a wrap springclutch.

FIG. 6B shows a top view of the device shown in FIG. 6A when assembled.

FIG. 6C shows a cross sectional view along section AA shown in FIG. 6B.

FIG. 6D shows details of a spring and a spring capture ring of thedevice shown in FIG. 6A.

FIG. 7A illustrates a two speed gear box using wrap springs withelectrolaminate tails.

FIGS. 7B, 7C, 7D, 7E, 7F, and 7G illustrate in detail various operatingmodes of the device depicted in FIG. 6A.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying figures, which form a part hereof. In the figures, similarsymbols typically identify similar components, unless context dictatesotherwise. The illustrative embodiments described in the detaileddescription, figures, and claims are not meant to be limiting. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the scope of the subject matter presented herein. It willbe readily understood that the aspects of the present disclosure, asgenerally described herein, and illustrated in the figures, can bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein.

I. OVERVIEW

Some embodiments of the present disclosure provide efficient,light-weight, compact and fast switching multispeed or variabletransmissions which can be applied in robotic manipulators. Multispeedor variable transmissions have been developed for a variety ofapplications but have not been widely used in robotics due to theircomplexity, volume and weight.

In some robots, since the speeds and torques of robotic manipulators arehighly cyclical and variable, using fixed gear ratio transmissionsresults in high energy inefficiencies because the motor is operatingaway from its optimum efficiency mode. It also limits the range offorces and speeds at which the manipulator can operate, forcing thedesigner to oversize the motors in order to meet worst case conditions.With a fixed gear ratio, conventional gear boxes do not allow dynamicmatching of the load impedance, leading to larger, heavier,less-efficient actuators. Just as a fixed-gear bicycle does not provideefficient locomotion in hilly terrain, a fixed-gear-ratio transmissionactuator limits the capabilities of a robotic joint and wastes energy.

Minimizing the time it takes to change gear ratios also leads toadvantages since constraints on the speed with which gear ratio maychange limits the speed at which the manipulator may change loads and asa result the range or tasks which it may accomplish. For example, for awalking robot the leg needs to move fast and with no load during theswing phase, but slower and with a higher load during the stance phaseof the walk. Similarly, in a pick and place robot, the manipulator mayneed to switch between carrying a heavy load at low speed and no load athigh speed, thus minimizing the cycle time.

Other advantages may be realized by being able to switch gear ratiosunder load and at zero speed to avoid limiting the range of tasks therobotic manipulator can perform.

Several innovative transmission techniques and mechanisms are describedherein. Common to the concepts described in this disclosure is the useof the electrolaminate effect. The electrolaminate effect, based onpreviously described electrolaminate technology, enables the clamping oftwo surfaces when a voltage is applied across the surfaces. This effectis used in various ways in the concepts within this disclosure.

Based on the electrolaminate effect, an electrolaminate disc clutch isdescribed. An electrolaminate disc clutch may be lightweight andcompact, thus lending itself to address the needs described above.Compared to existing means of engaging clutches, such as solenoids, theelectrolaminate clutch is lightweight, low-volume, and low power. Insome other concepts, various other types of clutches other than a discclutch are described. These include the wrap spring clutch and a bandclutch.

In yet other concepts, multi-speed gear box transmission systems aredescribed using the electrolaminate clutch technology. Briefly, in thesesystems, multiple electrolaminate clutches may be used to obtain ahigh-speed, low torque operation or low speed high torque operation.Combining the electrolaminate engagement system with a wrap-springcomponent allows the clutch to be scaled to larger torques than theelectrolaminate component could support independently.

Several benefits may be realized with the innovative clutches andtransmission systems described in this disclosure. The small footprintof the electrolaminate clutch allows designing a very compact singlespeed or multispeed transmission with a low number of parts. The clutchcan be easily integrated with a planetary gearhead design without addingmuch volume or weight to it. Typical on-market multispeed gear boxes areexpensive and bulky. Due to their bulk and expense, the on-market gearboxes may not be suitable for integration with a robotic system,especially one that is intended to be mobile. The electrolaminateclutches provide a mechanism by which gearing may be achieved with thinand light weight components. Yet another benefit is that thelight-weight clutch allows rapid engagement at a millisecond rateenabling a rapid actuation of the clutch. Since the electrostatic clutchengages with a flat surface (instead of a toothed surface, for example),it can engage disengage under load and at any speed.

An additional benefit is that the electromagnetic clutch is capacitivein nature, and therefore uses very little power when engaged. Whencompared to electromagnetic clutches, the electrostatic clutch uses upto three orders of magnitude less power, making it ideal for powerefficient applications.

The competition can be characterized by the various clutches that areavailable in the market now. However, none have the characteristic thatthe concepts described in this disclosure has in terms of low weight andbulk and being capable of being made with inexpensive parts andmanufacturing techniques.

II. ELECTROLAMINATE CLUTCHES AND TRANSMISSIONS—OPERATING PRINCIPLES

FIGS. 1A-C illustrate the operating principle of an electrolaminateclutch. The operating principle is based on the fact that oppositelycharged surfaces will experience a force of attraction towards eachother; thus if one surface rotates it will cause a second surfacecoupled electrostatically to the first surface to also rotate, giventhat a voltage is applied across the surfaces. A clutch can thus beformed by controlling the application of the voltage. If no voltage isapplied, the second surface will not be electrostatically coupled to thefirst surface and the rotation will not be transferred from one surfaceto another. The operating principle is described in detail in “Materialsfor Electroadhesion and Electrolaminate, US 20130010398A1”.

FIG. 1A shows one surface 10 of an electrolaminate clutch. This surfaceis typically flexible. The substrate of this surface is shown as 20 andmay consist of materials such as but not limited to polyimide, Kapton®,or Mylar®. A conductive layer 30 (or the electrode) is coupled on top ofthe substrate material. The conductive layer may be composed of metalsincluding but not limited to copper or silver. These electrodes may bepatterned or non-patterned on top of the substrate. A further layer 40of dielectric material is coupled to the electrode. The dielectricmaterial may be composed of materials such as but not limited topolyurethane.

FIG. 1B shows a configuration 11 where a pair of flexible surfaces asdescribed above with respect to FIG. 1A is placed so that the dielectriclayers of each surface face each other. FIG. 1B also shows an electriccircuit coupled to the conductive layers such that a capacitor is formedwith the two surfaces. The electrostatic force between the two surfacesis depicted by arrows 60. This force is also called the clamping forcein this disclosure. A second force that acts along the surface, theshear force, is also shown by arrow 70.

FIG. 1C shows another configuration 12 where the flexible surface isplaced against a metal surface 25. The metal surface may be rigid orflexible. In FIG. 1C, the metal surface is electrically grounded with apositive voltage being applied to the conductive layer 30. The sametypes of forces as described with respect to FIG. 1B exist with thisconfiguration as well.

Although specific configurations of applied voltages are shown in FIGS.1B and 1C, it is only necessary that a voltage potential exist betweenthe conductive layers of FIG. 1B or between the conductive layer and themetal layer in FIG. 1C. As an example, a voltage of +500V may be appliedto one side and a voltage of −500V may be applied to the other side.Other values of voltages are possible.

The flexible surfaces of the electrolaminate clutch such as 10 in FIG.1A may be as thin as 0.09″ or less. Other thickness values are notexcluded. The thinness allows these surfaces to flex and conform to theshapes of the opposing surface. This allows the surfaces to be in closeproximity to each other which ensures that the electrostatic clampingforce is very high. Consequently the torque transfer from one surface toanother is also high, making this an advantageous configuration for aclutch.

In FIGS. 1B and 1C, the clamping force is shown by arrows 60. If the twosurfaces were to be pulled away (or sheared) from each other (to theleft and right in FIGS. 1B and 1C), the friction between the surfaceswill counteract the pull force. The shear force indicated by arrow 70comes into effect in this situation. The shear force can be expressedby:

T _(s) =μT _(c)  Eqn. 1

where T_(s) is the shear force, μ is the coefficient of static frictionand T_(c) is the clamping force.

The coefficient of friction and the clamping force can both be variedindependently by using different types of materials, thickness ofmaterials and magnitude of voltage that is applied across thedielectric. This implies that the shear force can be varied by varyingthe coefficient of friction and the clamping force. This leads to theuse of an electrolaminate device in various applications. One broadcategory is the use of devices based on the principle described abovefor clutches which may then lead to design of light weight, low cost,efficient transmissions.

III. ELECTROLAMINATE DISC CLUTCH

FIGS. 2A and B describe the concept of the use of the electrolaminateeffect to form a clutch. FIG. 2A shows a motor 110 driving an axle 115which terminates with one surface of an electrolaminate clutch 121′. Thesecond surface 121″ is shown separated by a distance. The second surface121″ is also shown coupled to a gearbox 130 which is further coupled toa load 150 through an axle 140. An electrical circuit 160 is showncoupled to the surfaces 121′ and 121″ with the switch in the offposition. In this configuration, the motor 110 is not coupled to thegearbox 130 so even if the motor is turned on and rotates, no work isdone in terms of lifting the load 150.

In FIG. 2B, the switch in electrical circuit 160 is turned on and avoltage is applied to the surfaces 121′ and 121″. Due to theelectrostatic effect, the surfaces are now attracted to each other asexplained in FIG. 1. As long as an appropriate voltage is applied andthe surfaces are made of materials to provide sufficient appropriateclamping and shear force, the output of the motor is coupled to thegearbox which then lifts the load 150.

In one variation of the electrolaminate clutch, surfaces 121′ and 121″are thin and lightweight and conformable. For example, the surfaces maybe as thin as 0.09″. In another variation, the surfaces may be layeredand interleaved to increase the overall torque transmitted by theclutch. The interleaved configuration of the surfaces is illustrated inFIG. 2K and is described briefly later in this document. The entireweight of the clutch (including the two surfaces) may be less than 20 g.In comparison, on-market electromagnetic clutches of similar toquecapabilities are typically hundreds of grams.

FIGS. 2C and 2D illustrate more details about the electrolaminateclutch. Just as in FIGS. 2A and 2B, the two surfaces of the clutch inFIG. 2C are shown as 121′ and 121″. In FIGS. 2C and 2D, the disk 121′ isillustrated as the drive disk and disk 121″ is illustrated as the drivendisk. A spider spring 122, shown in FIG. 2D, couples the drive disk 121′to an input hub 123. The input hub may be coupled to an input motor by ashaft 129. The input hub 123 may be made of insulating material. A slipring 128 may be mounted on the input hub 123. The slip ring may be incontact with a brush 124 which may be pressed against the slip ring by aspring 125. Spring 125 may be held in a brush holder 126. An electricalconductor 127 may connect the slip ring to the spider spring 122. Theobjective of the brush holder 126, the brush 124, the slip ring 128, theelectrical conductor 127 and the spider spring 122 is to provide anelectric circuit to the drive disk 121′. The electric circuit itself isnot shown in FIG. 2C. On the side of the driven disk 121″, shaft 131 andbearings 132 provide support for disk 121″ to rotate. Bearings 132couple the shaft 131 to housing 133. The shaft 131, the bearings 132 andthe housing 133 may all be electrically conductive such that the disk121″ may be electrically grounded. When drive disk 121′ is energized,electrostatic attraction causes the drive disk 121′ to move towards121″. The spider spring 122 allows the disk 121′ to move towards 121″.These same electrostatic forces, acting through friction, cause thedriven disk 121″ to rotate when drive disk 121′ rotates. When disk 121′is de-energized, there are no attractive forces between the disks andthe spider spring causes the disk 121′ to move back, away from the disk121″ and the disk 121″ may no longer rotate. Hence in someconfigurations, a constant speed motor may cause the drive disk 121′ tokeep rotating but by energizing and de-energizing the electrical circuitin a specific sequence, the driven disk 121″ may be caused to rotate atany speed within the allowed range of 0 to maximum speed of the inputmotor. The energizing and de-energizing sequences are described in moredetail in the companion disclosure titled “Mechanically SwitchingInfinitely Variable Transmission”.

Yet other configurations of the electrolaminate disc clutch are nowdescribed. As specified earlier, one or both of the surfaces of theelectrolaminate clutch may be made of a thin flexible material.Challenges encountered when one or both surfaces of a clutch areflexible include how to make the clutch flexible enough to conformrapidly to the opposing surface and still rigid enough to transmitenough torque. The configurations below address the challenge. FIG. 2Eshows a cross section of the device using the electrolaminate clutch.205 is a motor held in place by a housing 210. The main shaft of thedevice is denoted by 220. To the right of FIG. 2E, 245 is generally amultispeed gearbox. The multispeed gearbox will be explained in detailbelow but for the purposes of this part of the discussion related to howto hold and configure the electrolaminate clutch, it is sufficient toassume 245 represents an output stage. Thus the output stage 245 iscoupled to a thin but rigid plate 235 via four pins of which only twoare shown as the figure is a cross sectional view. The two visible pinsare denoted by 240′ and 240″. The pins are only loosely coupled to thedisc 235. They fit inside holes which are slightly oversized; forexample if the pins are 0.063″ diameter, the holes may be 0.080″diameter. There may be more or less holes and pins, for example 3 or 6holes. The disc 235 may be made of plastic and may be as thin as 1/16″thick. Other thicknesses and materials are not excluded. This disc hasthe same number of holes around the edge to accommodate the pins. Inthis example, due to the assumption that the device 200 has four pins,the disc 235 will have four holes as well. This disc also has a largehole in the center to accommodate the shaft 220. Additionally, the discalso has a second smaller disc 215″, arranged concentrically about itsaxis as shown in the figure. The second disc 215″ and the larger disc235 may be made of one piece or it may be two pieces bonded together.Additionally, the second disc (215″) is bonded to one of surfaces 230″of the electrolaminate clutch. This surface (230″) is a very thin,flexible material, for example 0.09″ thick. It may be made of a thinpolymer substrate such as Kapton® with a layer of conductive electrodematerial such as copper and a layer of dielectric polymer encasing theelectrode. The second surface 230′ of the electrolaminate clutch issimilarly bonded to a second small disc 215′. This second small disc215′ is coupled to a metal mount 225 which is coupled to bushing 250made of insulator material. The bushing insulates the metal mount 225from the metal axle 220. However, the bushing and therefore the metalmount, the disc 215′ and the surface 230′ are coupled such that they arealways spinning with the motor and at the speed of the motor. The metalmount 225 may be connected to an electrical circuit via a bush, or aroller, depicted by 255. Surfaces 230′ and 230″ of the electrolaminateclutch are also discs and their diameter is larger than the diameter ofdisc 215′ and 215″ but smaller that the pin to pin distance between 240′and 240″.

For the electrolaminate clutch to work, torque has to be transmittedfrom one surface to another. In this case, torque needs to betransmitted from surface 230′ to 230″ in order to transmit torque fromthe input (motor) to the output (output of the gearbox). The surfacesneed to be in very close proximity to each other to begin with forexample less than 0.5 mm apart, for the electrostatic attraction betweenthe surfaces to overcome other forces and couple the surfaces together.Any misalignment of either of the two surfaces in any direction willreduce total area of the surfaces that can touch each other, reducingthe electrostatic coupling and thus reducing the amount of torque thatcan be transmitted before the clutch slips. An example of themisalignment is if the second surface 230″ is skewed along the axis ofthe shaft such that in relation to how the figure is drawn, the surface230″ may not be vertical. Another example of misalignment is if thesecond surface is slightly rotated around an axis perpendicular to theaxis of the motor. Alignment issues may occur with the surface 230′ aswell. Further, alignment issues may be caused by imperfections in theshape of the surfaces themselves. The reason why misalignment causes adecrease in the maximum torque that is possible to transfer is due tothe fact that the electrostatic forces are strong when the surfaces arein contact with each other but are quite weak when there is anyappreciable distance between the surfaces or sections of the surfaces.Thus the structures that hold the surfaces have to be such that theyallow the two surfaces of the electrolaminate clutch to conform to eachother's shape, thus overcoming misalignments. Specifically, referringback to the figure, the reason the surfaces 230′ and 230″ can self-alignthemselves with very little extra force is because surface 235 is onlycoupled loosely to the pins 240′, 240″, 240′″ (not shown) and 240″″ (notshown). By being loosely coupled (in other word by not restricting themotion of the surface 235 within a certain range), the pins and supportdisk 235 allow the two planes of the clutch 215′ and 215″ to be paralleleven if there is some skew between the faces of disk 225 and the gearbox245. When a voltage is applied across the surfaces 230′ and 230″ (thetwo surfaces of the electrolaminate clutch), since they are in closeproximity to begin with and flexible, the surfaces 230′ and 230″ willconform to each other's shape, which may be a more complex shape than asimple plane. In addition to the loose coupling of the plate 235 withthe pins, the plates 215′ and 215″ play an advantageous role in thealignment of the surfaces 230′ and 230″. The advantage is realized dueto the diameter of the plates 215′ and 215″ being smaller that thediameter of the surfaces 230′ and 230″ of the electrolaminate clutch. Tounderstand why, it is easier to think about the consequences of mountingthe flexible surfaces of the electrolaminate clutch on a rigid base withthe same diameter as the plates. When mounted on a rigid base, theability of the flexible surfaces to conform to each other's shape isdiminished or removed altogether. If there are any imperfections inshape, the surfaces or at least sections of the surfaces will not be inclose proximity to each other and the ability to transmit torque may bediminished. These effects are explained in more detail in US2013/0276826by some of the same authors of this disclosure.

The design of the clutch for example the choice of the diameters of theplates 215′ and 215″ relative to the diameter of the electrolaminatesurfaces, the stiffness of the electrolaminate surfaces must be suchthat the maximum torque is transmitted with the least possible weightand bulk of the clutch. The design must be such that the clutchovercomes the various failure modes. One failure mode is associated withbuckling of the electrolaminate surfaces. As explained above, theelectrolaminate disks will adhere to each other over more surface areaif the plates supporting them (215′ and 215″) are small in surface area.As the plates 215′ and 215″ are rigid, the electrolaminate surfaceseffectively do not adhere to each other over the surface where the backside of the electrolaminate surface is adhered to the rigid supportplate 215′ or 215″ because they cannot conform to each other. Thisargues for small support plates in order to maximize the area ofelectrolaminate clamping and thus maximize the torque that can betransmitted. However, because the electrolaminate surfaces are thin andflexible, they will buckle or wrinkle if too much torque is applied. Theonset of buckling is dependent on the stiffness of the electrolaminatesurfaces, their materials, and the diameters of the electrolaminatesurfaces and the support plates 215′ and 215″. If buckling occurs, itmay limit the maximum torque capacity of the clutch, rather than theother failure modes which will be discussed next. The parameters thataffect buckling mentioned above must be so chosen that buckling does notoccur given the application the clutch is being used for. Theapplication will determine among other factors, the anticipated load,the speed at which the motors have to rotate, the size the clutch andindeed the entire drive mechanism ought to be.

Yet another failure mode is associated with the surfaces of theelectromagnetic clutch 230′ and 230″ slipping relative to each other.Slippage may occur when the electrolaminate clamping force is thelimiting factor. However to prevent slippage from occurring, the totalmaximum theoretical torque transmission of the electrolaminate clutch(assuming no buckling) may be evaluated. The equations for this maximumtorque are given below. FIG. 2I shows a small patch at a distance r fromthe center of the electrolaminate surface. The maximum torque that canbe transmitted by a small patch is given by the shear force Fs×r (thedistance between the central axis and the patch). This suggests thatpatches further from the central axis of the device have the ability totransmit more torque (for a given maximum electrolaminate clampingforce) than patches close to the central axis. FIG. 2J describes theprocedure for calculating the theoretical maximum torque that may betransmitted by a surface with an annulus of electrolaminate surface asshown in the configuration in FIG. 2E.

Here:

Fs is the shear force acting on a small patch,

μ is the coefficient of static friction,

F_(N) is the normal force the patch experiences,

P_(N) is the normal pressure the patch experiences,

r is the radial distance of the patch from the central axis,

R₁ is the radius of the disk 215′ or 215″ (or the inner radius of theannulus of electrolaminate surface),

R₂ is the outer radius of the electrolaminate surface,

dr is the infinitesimal width in the radial direction of a ring,

n is the number of interfaces that make up the clutch (FIG. 2E shows 1interface; however, there may be multiple electrolaminate clutchinterfaces, each with one side coupled to the input shaft and one sidecoupled to the output), and

T is the total theoretical maximum torque transmitted by theelectrolaminate clutch.

Hence since

F=PA  Eqn. 2

The shear force acting on a ring at a distance r from the center is:

F _(S) =μF _(N) =μP _(N) n2πrdr  Eqn. 3

The theoretical maximum torque that a ring or disk clutch may transmitis (R₂ and R₁ define the limits of the available area for torquetransmission):

T=μF _(S) r=∫ _(R) ₁ ^(R) ² μP _(N) n2πr ² dr  Eqn. 4

Thus, carrying out the integral, the theoretical maximum torquetransmitted by the electrolaminate clutch is

$\begin{matrix}{T = {\mu \; P_{N}n\; 2\; {\pi\left( \frac{R_{2}^{3} - R_{1}^{3}}{3} \right)}}} & {{Eqn}.\mspace{14mu} 5}\end{matrix}$

Thus it can be seen by Eqn. 5 that to maximize T, R₂ has to be maximizedand R₁ needs to be minimized. Moreover, Eqn. 5 shows that for a givenamount of clutch surface area, the torque capacity of the clutch can bemaximized by situating this given surface area at a large radius (farfrom the central axis of the device). Eqn. 5 may also be used to limitthe torque (by choosing the radii appropriately) that may be transferredin order to prevent failure modes. Finally, Eqn. 5 also suggests thatthe advantageous configuration of the electrolaminate surface and thestiff backing plate is such that that the stiff backing plate is placedconcentrically near the axis of rotation rather than having a stiffbacking plate towards the outer edge of the electrolaminate surface.

These three design considerations (maximize electrolaminate clampingarea, minimize buckling, and maximize clamping at large radii) lead tothe design of the disk clutches as described above with spacer plates215′ and 215″. Typical dimensions that satisfy these designconsiderations are as follows. The spacer plate 215′ and 215″ are about0.8″ diameter, the electrolaminate surfaces 230′ and 230″ are about 2″diameter, and the thickness of the electrolaminate surfaces is about0.009″.

An alternate configuration to device 200 of FIG. 2E is shown is FIG. 2F.Here the only difference is that the surface 230′ and disc 215′ areremoved. Instead the surface 265 of the metal mount 225 acts as anelectric ground. Thus in this configuration, instead of having twoflexible surfaces, there is one flexible surface (with dielectricmaterial coated or deposited on it) and one rigid surface; however whenvoltage is applied across the flexible surface and the grounded surface,since the flexible surface can conform to the shape of the rigidsurface, efficient torque transfer is obtained.

An alternate configuration to device 260 of FIG. 2F is shown in FIG. 2G.Here a light weight wave spring 275 is included behind the plate 235 sothat the surface 230″ of the electrolaminate clutch may always be inloose contact with the electrically grounded surface 265. Thisconfiguration will increase the friction between the grounded surfaceand the surface 230″ when the voltage is off but this increase is smalland in the order of the friction generally encountered between brushesand rotating components such as axles in motors. However, the advantageof including the spring in the configuration 270 is that fasteractuation times may be provided since the surface of electrolaminate andthe ground are already in close proximity.

FIG. 2H is an exploded view of the actual clutch assembly. 235 is thelightweight rigid disc as explained above. It is shown to have fourholes; only one hole is enumerated as 277 but all four holes arevisible. These are the holes the pins 240′, 240″, 240′″ and 240″″ gothrough. 280 is the large hole that the shaft 220 goes through. 215″ isthe small disc that separates the plate 235 from the electrolaminatesurface. The disc 215″ is mounted concentrically on 235 and is also thinand made of lightweight materials such as plastic. The thickness of thisplate may be less than 1/16″ although no limitation is intended. Disc282 is the part of 230″ (one of the surfaces of the electrolaminateclutch) and is the backing or substrate and the electrode. It may bemade of a sheet of polymer over which the electrode may be printed. Theelectrode may be printed only on one surface as shown by 283, and maycover some or all of the surface indicated. For example, the electrodemay have a thin border of non-printed substrate material around it, toencapsulate the majority of the electrode within the electrolaminatesurface 230. Various ways for printing or etching such electrodes onflexible substrates have been developed for electrical flex circuitdesign and are well-known in the art. The disc 282 also has a tab 285which is coated with the same conducting material as used for theelectrode so that the electrode can be powered. The tab may be bent overthe disc 235 and may be coupled to the metallized housing of 245, theoutput stage. An alternate arrangement instead of having the tab 285 isto drill a via and connect the electrode printed on surface 283 throughthe via to the backside of disc 282. A wire may then be coupled to thevia on the backside of the disc for example by soldering. This wirewould then be connected to an electrical circuit just as the tab 285would be connected. The location of the via may be advantageously placedas close to the center of the disc as possible. The via and the locationof the via may cause the disc to experience less stress around the viacompared to the stress it may experience due to the tab. This couplingmay be as simple as taping the tabs to the metallized housing or sometype of conductive paste may be used to bond the tab to the metallizedhousing. Not shown in the figure, but brushes or slip rings may then beused to provide power to the metallized housing which would then providepower to the electrode. 287 is a dielectric layer that is then appliedon top of the electrode. Not included in FIG. 2H is the second surface230′ of configuration 200 in FIG. 2E. However the design of this surfaceis similar to the design 230″ described in FIG. 2H. If tabs areutilized, the tabs of the plates 230′ would be folded over and bonded tothe mount 225 thus providing connections to an external circuit. If viasare utilized, a wire bonded to the via would be coupled to mount 225just as the tab may be bonded.

An alternate construction of the clutch surfaces is illustrated in FIG.2K. Instead of the clutch having flexible almost planar surfaces asdescribed previously it may assume a configuration as shown in FIG. 2K.The configuration generally has two members 290 and 294. Member 290 mayhave two concentric segmented drums illustrated by 292 and 293. Only onesegment (291) is enumerated. The segments of the drum 292 and 293 may bemade of thin flexible material of the type described in FIG. 1A. Drum294 is a hollow structure made of rigid walls. The drum 294 may be madeof lightweight materials such as aluminum. The diameter of the drum 292is such that it fits between the two segmented drums 292 and 293. Themembers 290 and 294 are coupled to shafts depicted by 295. In thefigure, and only as one possible configuration, drum 294 is made ofmetal and is electrically grounded and 290 and the drums 292 and 293 arecoupled to a positive voltage of +V. The dielectric layer on drum 292may be on the inside diameter and the dielectric layer on drum 293 maybe on the outside diameter. With such a configuration, when drum 294 isinserted in between the space between the drums 292 and 293 and when thevoltages are applied as specified, the segments of 292 and 293 will beattracted electrostatically to the drum 294, as long as the initialspacing (before application of the voltages) between the drums is verysmall such as less than 0.5 mm. Now if either 290 or 294 were to becoupled to a motor, upon application of the voltage, torque will betransferred from one member to the other. As more surface area forcoupling is provided by this configuration compared to theconfigurations in the previous examples, the torque transfer will belarger.

Many variations of the configuration shown in FIG. 2K are possible.Member 290 may have more than two segmented drums and subsequently drum294 may also have multiple inner drums to interleave between the drumsof 290. Member 294 may be made flexible and member 290 may be maderigid. Voltages other than +V and ground may be applied. The dielectricmay be applied to only one side such as the inner diameter of the drumsof 290.

As an alternative to the above structures described in FIGS. 2E-H, toensure efficient transmission of torque, all the components of theclutch may be manufactured with very tight tolerances through precisionmachining. However this type of precision machining will be expensive,driving up the cost (and weight as plastics may not be a suitablematerial for precise machining) of the transmission system. The methodsdescribed above allow the transmission of torque using lightweightmaterials without the need for precision machining.

In another concept, the electrolaminate clutch may be switched off andon at a rapid rate. For example the clutch may be switched on and off athigh speeds for example at 50 Hz. The clutch may work at other speedssuch as but not limited to 10 Hz, 20 Hz and 25 Hz. Typical on marketdevices may work at 25 MHz. In another variation, since the mass of theclutch is small, the transient response i.e. the time period when theload is becoming engaged to the motor or when the load disengages fromthe motor is also small. A comparison of an electrolaminate clutchdescribed in this disclosure against a typical commercially availableelectromagnetic clutch is illustrated in Table 1 below.

TABLE 1 Example Typical Electrolaminate On-Market Specification UnitClutch EM Clutch Clamping Pressure MPA/(psi) 0.35 (50) N/A Coefficientof Friction — 0.2 N/A Shear Pressure MPA/(psi) 0.07/(10) N/A Nm/g 1 0.08Torque/Volume Nm/cm³ 0.5 0.018 Engagement Time msec 1-100 20 ReleaseTime msec 1-100 20 Power W 0.004 3.4 Voltage V 400 24 Current μA 10142000 Materials Kapton ® with Permanent magnets patterned

The values of the parameters shown in the table above for the ExampleElectrolaminate Clutch are example values for one configuration of theclutch but other values of parameters are possible. However, it isinstructive to compare some parameters which exhibit the advantages ofan electrolaminate clutch. For example the torque to weight ratio is 1for the electrolaminate clutch but is 0.08 for a typical on-marketelectromagnetic clutch. Another example is that the power consumptionfor the electrolaminate clutch is 0.12 W whereas the typical EM clutchhas a power consumption of about 3 W. FIGS. 2A-D illustrate atransmission system with one electrolaminate disk clutch. Now, a systemwith two electrolaminate clutches is described in detail in FIGS. 3A-D.

IV. MULTISPEED GEARBOX USING ELECTROLAMINATE DISK CLUTCH

FIGS. 3A-D illustrate a multispeed gearbox using electrolaminateclutches. In one concept, the multispeed planetary gear box transmissioncan be electronically switched to quickly adapt its gear ratio tochanging load requirements. In another concept, the multispeed gearboxdescribed below allows more efficient power management by closelymatching the impedance of a motor to the varying load impedance.

Referring to FIG. 3A, a motor 310 is shown with an axle 315. The axle315 supports adisc 318 upon which one surface of an electrolaminateclutch 330 is coupled to. The second surface of 330 is coupled to a ringgear 335, which has teeth on the inside diameter. The ring gear iscoupled to multiple planetary gears 325′, 325″ and 325′″, each of whichis coupled to a sun gear 320. The section AA′ of the multispeed gearbox300 is shown in FIG. 3B where the sun gear 320, the planetary gears325′, 325″ and 325′″, and the ring gear 335 are all illustrated moreclearly. For clarity, no teeth are illustrated in FIG. 3B. The gearboxshown in FIG. 3A has two electrolaminate clutches 330 and 350. It alsohas three stages of gearing, gearing stage 360, gearing stage 345 andgearing stage 335. Gearing stage 335 and 345 are coupled to the samering gear 340 so essentially these two gearing stages form one gearboxillustrated as 327 in FIG. 3A. There may be fewer or more gearing stageswithin gearbox 327. The final gearing stage is illustrated as 360. Thefinal gearing stage also has a ring gear 355 and a set of sun andplanetary gears such as illustrated in FIG. 3B. As illustrated in FIG.3A, the ring gear 355 is always grounded meaning that it is alwaysstationary. The gearing ratios may be different for the output stagecompared to the ratios provided by the gearbox 327. Although only onegearing stage 360 is shown, there may be more gearing stages.

FIGS. 3C and 3D illustrate how the device 300 may work. In FIG. 3C,electrolaminate clutch 350 is closed which is accomplished by applyingan appropriate voltage across the surfaces of 350. This action groundsor holds the ring gear 340 stationary. The output of gearbox 327 willthen be determined by the gearing stages 335 and 345. This output isfurther geared by the final output stage 360 and the final gear ratiowould be thus be a product of the gear ratio of the final output stage360 and the gear ratio of the gearbox 327.

In FIG. 3D, electrolaminate clutch 330 is closed and electrolaminateclutch 350 is open. The ring gear 340 now spins with the motor shaft315. Since the motor shaft 315 is always spinning, the entire gearbox327 with all its gearing stages spins with the motor shaft and thusproviding a gear ratio of 1:1 at the output. The final gear stage 360 isthe only gear stage that provides a ratio not equal to 1:1 at its (thefinal) output.

The utilization of this device is now described. If high speed, lowtorque operation is required, electrolaminate clutch 330 is turned onand electrolaminate clutch 350 is turned off (FIG. 3D). If low speed,high torque is required, electrolaminate clutch 330 is turned off andelectrolaminate clutch 350 is turned on (FIG. 3C). Since the clutchescan be turned off on and rapidly, the final output conditions can beaccommodated rapidly as they are encountered.

V. ELECTROLAMINATE BAND CLUTCH

FIGS. 4A-C illustrate yet another concept of a clutch utilizing theelectrolaminate effect. In these figures, two wheels 410 and 420 areshown with a band or belt that goes around the two wheels. Wheel 410 isindependently actuated for example by a motor and is illustratedspinning in the direction of the arrow 470. Wheel 420 is notindependently actuated and depends on the transmission of tension bymeans of the band or belt 430. In the particular example, the wheels 410and 420 have flat surfaces over which the belt is placed. In particular,they have no gear teeth. However, both wheels have a coated surface 490and 495 clearly illustrated in FIG. 4C each of which may form onesurface of the electrolaminate clutch individually. The band or beltforms the second surface of the electrolaminate clutch. When the switch450 in the electrical circuit 440 is off (FIG. 4A), the band or beltcouples loosely over the wheels 410 and 420. No tension is transmittedfrom wheel 410 to wheel 420. When the switch 450 is turned on (FIG. 4B),the band or belt couples tightly to the wheels due to the electrostaticeffect. Now tension is transmitted from wheel 410 to 420 and wheel 420starts to also rotate. The advantages of the electrolaminate clutchdescribed earlier such as being lightweight, being able to achieve rapidengagement and disengagement, and being inexpensive apply to bandclutches as well.

In some concepts, the wheels do not need to be of the same diameter. Insome other concepts, there may be more than one unactuated wheel. In yetother concepts, the band or belt need not be straight as shown—they maybe twisted. In other concepts, the band can be at high potential and thewheels can be at the lower potential (or vice versa).

VI. ELECTROLAMINATE WRAP SPRING CLUTCH

FIGS. 5A-B illustrate yet another concept of a clutch utilizing theelectrolaminate effect. Referring now to FIG. 5A, two shafts 610 and 620are shown. Shaft 610 is an input shaft such that it may be actuated by amotor or other device or it may itself be part of an actuator. Shaft 620is the output shaft which may be further connected to other componentssuch as but not limited to gears, pulleys and loads. Spring 640 couplesshaft 610 and output shaft 620 such that in an assembled configuration,the device 600 may appear as illustrated in FIG. 5B. Shaft 610 and 620may be in close contact with each other within the spring 640. Theinside diameter of spring 640 may be slightly larger (e.g. 0.2 mm) thanoutside diameter of the shaft 610 but may be slightly smaller (e.g. 0.2mm) than the outside diameter of output shaft 620. Spring 640 may havean extension 650 which may be mechanically placed under a ring 630 asshown in FIG. 5B. An electrical circuit 660 may be connected to the ring630 and input shaft 610 as shown in FIG. 5A via slip rings and brushes(not shown in the figure). The ring 630 may form one side of anelectrolaminate device with the other side being the input shaft 610.

In operation, when the electrical circuit 660 is open, the input shaft610 may freely rotate within the spring 640. The input torque is notcoupled to the output shaft 620. When electrical circuit is closed, thering 630 couples tightly to input shaft 610 which causes the spring toclamp down on the input shaft, thus causing the spring to rotate in thedirection of the input shaft. The torque is transmitted through thespring to the output shaft 620 which now begins to rotate. The maximummagnitude of the torque applied to the output shaft through the springis determined by the Capstan equation which includes the effect ofhaving a variable number of turns. This equation is given below as Eqn.6:

T _(load) =T _(hold) e ^(μ) ^(θ)   Eqn. 6

where T_(hold) is the applied tension generated by the clampedelectrolaminate ring, T_(load) is the resulting force exerted at theother side of the capstan and θ is the total angle swept by all theturns of the spring. The combination of the spring with theelectrolaminate ring allows the maximum torque of the clutch to exceedthe maximum torque that the electrolaminate ring would be able towithstand alone.

In other variations of the concept, more than one spring may beutilized. The additional springs may be wrapped in opposing directionssuch that torque may be transmitted in clockwise or counter-clockwisedirections.

VII. DETAILED DESCRIPTION OF A DEVICE USING WRAP SPRING CLUTCH

FIGS. 6A-C illustrate the details of a clutch using a wrap springmechanism. FIG. 6A is an exploded view. FIG. 6B is the top view and FIG.6C is the cross sectional view along section AA. The input of the deviceis shown as member 725. This member may be coupled via slots to anexternal source such as a motor. The motor is not shown in the figure.Members 725, 720 and 715 may thus rotate continuously when the externalmotor is coupled and rotating. The function of member 715 and 720 willbe explained below. Input member 725 may also be coupled to theelectrolaminate mount 760 such that it too rotates when an externalinput is applied. The function of the electrolaminate mount is to keepthe electrolaminate sheet 750 in place by means of a coupling nut orscrew 755 which couples the electrolaminate mount to theelectrolaminate. The coupling nut or screw 755 is seen clearly in FIGS.6B and 6C. The electrolaminate is shown as a thin dark rectangle in FIG.6C but is not included in FIG. 6B so that the coupling screw or nut maybe seen clearly. Member 765 is the power electrical power drum whichsupplies power to the electrolaminate via brushes which are not includedin the figure for clarity. On the output side, member 730 forms theoutput. Member 730 is seen clearly in FIGS. 6A and 6C. Member 730 may becoupled rigidly to a wrap spring 735. The spring is shown separately inFIG. 6D to show clearly that it has a tab or a tail at its end. The tailof the spring is shown as member 736. When assembled, the tail of thespring may fit in a groove 741 in a spring capture ring 740 such thatwhen the spring capture ring rotates, the spring will rotate. Referringback to FIG. 6A, when assembled, the wrap spring may be positioned overthe surface 715 which forms part of the input side as specified earlier.Also when assembled, the spring capture ring 740 may be positioned oversurface 720 but may slide over this surface. When the spring capturering rotates, the wrap spring may clamp down on the surface 715. If theinput is rotating, then the clamping action will cause the spring torotate which will cause the output 740 to rotate.

The spring capture ring may be rigidly coupled to the electrical grounddrum 705. When assembled, the electrical ground drum may be positionedunder the electrolaminate 750. The position of the electrical grounddrum may be clearly seen in FIG. 6C. The electrical ground drum may beconnected to electrical ground by brushes (not shown in the figures).The electrical ground drum forms the companion surface to theelectrolaminate sheet 750 such that the sheet may clamp on to thesurface of the electrical ground drum due to the electrostatic forcebetween the laminate and the drum. Any motion of the electrolaminate maythus be imparted to the drum. As described earlier, the electrolaminatedrum may also rotate with the input. Thus, if the input rotates and if avoltage is applied to the electrolaminate sheet, the electrical grounddrum may also rotate. When the drum rotates, the spring capture ring 745rotates, which will cause the output 730 to rotate as explained earlier.Thus by controlling when voltage is applied to the electrolaminate, theinput rotation may be coupled to the output.

VIII. TWO-SPEED TRANSMISSION SYSTEM USING THE ELECTROLAMINATE WRAPSPRING CLUTCH

FIGS. 7A-G illustrate a two speed transmission system using the wrapspring clutch. This type of implementation may be used for examplewithin a shoulder joint of a humanoid robot, where the motor within theimplementation can pull or be powerful in only one direction but canrotate clockwise or counterclockwise. In such a system, the motor mayalways pull on components it is coupled to such as but not limited tocables and tendons.

FIG. 7A illustrates a cross section of the motor. FIG. 7B describes thevarious modes of operation of the motor. FIG. 7C illustrates that themotor can achieve low or high gear reduction ratios. And FIGS. 7D-Gillustrate in more detail how various modes may work.

Referring to FIG. 7A, a motor is shown as 805 with a shaft 810, a drum820 coupled to the shaft, a sun gear 835. The sun gear 835 is coupled toa planetary system with planet gears 830′ and 830″. A third planetarygear 830′″ is not shown. The planet gears rotate within a ring gear 850.A planet carrier 840 is shown such that it couples to the planet gears830′, 830″ and 830′″ (830′″ is not shown). The planet carrier carriesthe motor output 844. The planet carrier is also coupled to a planetcarrier drum 842; this drum is the same size as the drum 820 and it alsorotates about the shaft 810. The housing of the ring gear 850 is coupledvia a wrap spring 825 to the motor housing 850. As in device 600, thewrap spring 825 may have an extension which may be placed under a ringwhich may be located over the motor housing, in close proximity to thespring. The ring may form one side of the electrolaminate device whereasthe motor housing may form the other side. The ring may be connected toan electrical circuit via brushes or slip rings. The motor housing isstationary and it can be connected easily to the other side of anelectrical circuit. When a voltage is applied across the ring andhousing, the ring can clamp down on the housing causing the springextension (located under the ring) to also be stationary. The spring 825is always coupled tightly to the housing of the ring gear 850; howeverthe internal diameter of the spring 825 is such that it is slightlylarger (e.g. 0.1 mm to 0.5 mm) than the external diameter of the motorhousing. The external diameter of the motor housing is indicated byarrows 845 in the figure. Upon application of a high voltage, theextension of the of the wrap spring 825 under the ring may coupletightly with the motor housing. As the motor housing is fixed to ground,it cannot rotate. Thus when the high voltage is applied to the ring, thering gear is also not able to rotate.

A second wrap spring 875 with an electrolaminate activated ring is alsoincluded and couples the planet carrier drum 842, the drum 820 andanother housing 870—a housing of a one-way roller clutch—in thefollowing way. The internal diameter of the spring wrap 875 is such thatit passively couples the planet carrier drum 842 and the drum 820. Inother words, the internal diameter of the wrap spring is smaller thanthe outside diameter of the planet carrier drum 842 indicated by arrow860 and also is smaller than the outside diameter of the drum 820indicated by the arrow 855. This arrangement of diameters is such thatthe planet carrier drum 842 and drum 820 are passively engaged to eachother. The ring of the spring 875 is placed over the housing of theone-way roller clutch 865 and may be activated using the electrolaminateeffect.

If wrap spring 875 is not activated, since the drum 820 and the planetcarrier drum 842 are passively engaged, if the motor turns in thedirection of the wrap spring, for example if the spring wind directionis clockwise and the motor spins clockwise, then the output 844 followsthe motor without any gear reduction. The clockwise spring winddirection is used as an example—the spring may be wound in thecounterclockwise direction and the opposite situation as described abovemay occur with regards the motor direction and output. Continuing withthe example of the spring wind direction in the clockwise direction andassuming still that the wrap spring 875 is not activated, if the motorspins in the counter-clockwise direction, this rotation will not becoupled to the output. However if the output spins in thecounter-clockwise direction, the output is able to back-drive the motor.The description of the operation of the device 800 when wrap spring 875is activated will be described later, after describing the operation ofthe device when wrap spring 825 is activated.

Spring 825, as described earlier, is always coupled to the ring gear850, but its ring has to be activated for it to couple to the motorhousing 850. Spring 825 needs to be activated if a gear reduction isrequired. In the situation where the spring 825 is not activated, thering gear 850 will rotate with the planetary system and the output isdescribed above. In the situation where the spring 825 is activated, thering gear cannot move as the spring clamps down on the motor housing,locking the ring gear to the motor housing. To ensure that the planetcarrier rotates such that a gear reduction is obtained at the output,the planet carrier drum 842 has to be decoupled from the drum 820. Thisis achieved by activating the spring 875, which as described earlier,has an electrolaminate ring over the housing of the one-way roller 865.If this ring is activated, the ring is held in place and the planetcarrier drum 842 decouples from the drum 820 and does not rotate withdrum 820. The rotation of the planetary gears 830′, 830″ and 830′″(830′″ is not shown) is caused by the rotation of the sun gear 835. Inthis situation, when the outer ring gear 850 is stationary, the output844 experiences a gear reduction as given by Eqn. 7:

$\begin{matrix}{r = \frac{1}{1 + \frac{N_{r}}{N_{s}}}} & {{Eqn}.\mspace{14mu} 7}\end{matrix}$

where N_(r) is the number of ring gear teeth and N_(s) is the number ofsun gear teeth.

In the situation where wrap spring 825 is activated, and the output isrequired to back-drive the motor (i.e. cause the motor to spin in thecounter clockwise direction as an example), the ring of the spring 875needs to be allowed to spin in the direction of the back-drive(counter-clockwise for example). Hence, a one-way roller 880 is includedsuch that in this specific situation where the output is back-drivingthe motor, the ring of the spring 825 is clamped to the housing of theone-way roller (thus decoupling the planet carrier drum 842 from thedrum 820), however the one way roller is able to roll counter clockwiseover the motor housing 850. The shaft 835 may spin counter clock-wisefaster than the planets (also spinning counter clockwise) due to thegear reduction ratio but that does not cause any issues as far asachieving back drive is concerned.

FIG. 7C describes the various situations described above. The figureillustrates that in region A and D, a gear reduction ratio is obtainedby turning on both clutches or activating the springs. In region A, themotor is driving the output but in region D, the load back drives themotor but using an overrunning clutch as explained above. In regions Band C, the clutches are off and the device operates at no gearreduction. In region B, the motor drives the load and in region C, theload back-drives the motor.

FIGS. 7B, 7D, 7E, 7F, and 7G describe the various modes the device caninteract with the load, regardless of the gear reduction ratio.

Mode 1: Motor applied torque direction is clockwise, motor direction isclockwise.

Referring to FIG. 7D, in this mode, the load is being lifted (in thisexample in the counter clockwise direction) and torque is being appliedto the load by the motor also in the counter clockwise direction. Themotor rotates in the counter clockwise direction as well. For no gearreduction, the spring clutches are not engaged. For gear reduction, theclutches are engaged. This mode is indicated as “Mode 1” in FIG. 7B.When the clutches are on, the device 800 is in Region A in FIG. 7C. Whenthe clutches are off, the device 800 is in region B.

Mode 2: Motor applied torque direction is clockwise, motor direction iscounter-clockwise (Controlled fall).

Referring to FIG. 7E, the load is lowered but at a controlled rate. Themotor is still applying torque in a clockwise direction to achieve thecontrolled fall however the motor is allowed to turn counter clockwiseto allow to load to be lowered. When the clutches are off, the device800 is in Region C in FIG. 7C. When the clutches are on, the device 800is in region D.

Mode 3: Direction of torque from the load is counter-clockwise, motordirection counter-clockwise.

Referring to FIG. 7F, the motor is not applying any torque. It is simplyallowing the load to back drive. Another agent such as another motor oranother actuator may be pulling on the load as indicated. When theclutches are off, the device 800 is in Region C in FIG. 7C. When theclutches are on, the device 800 is in region D.

Mode 4: Direction of torque from the load is counter-clockwise, motordirection clockwise (No slack condition).

Referring to FIG. 7G, as in mode 3, another agent such as another motoror another actuator may be pulling on the load as indicated. The motoris illustrated as turning in the clockwise direction to obtain suchstates as a no-slack condition. It may be resisting the torque appliedby the external agent as well. Both the motor and the load may berotating in a clockwise direction, but the load is decelerating thesystem. When the clutches are on, the device 800 is in Region A in FIG.7C. When the clutches are off, the device 800 is in region B.

Hence it is now explained how the four different modes of FIG. 7B may beachieved along with the operations in the four different regions of FIG.7C.

With the forgoing discussion, it can now be seen how electrolaminatesmay be utilized to make clutches which have many advantageousproperties.

IX. SUMMARY CONCEPTS

Example concepts related to this disclosure include:

A first concept of a method of coupling an input stage to an outputstage by utilizing two surfaces, at least one of which is flexible andthin (less than 0.5 mm), which may be electrostatically clamped togetherwhen a voltage is applied across the two surfaces. When clamped, theinput rotation is imparted to the output stage which also begins torotate. When the voltage is turned off, no rotation is imparted to theoutput stage.

The method of the first concept, where a first surface is coupled toelectrical ground and where a second surface is coupled to an electricalpower source via a brush or a slip ring and where the second surface isalso coupled to a spider spring. When no voltage is applied, the twosurfaces are separated but when a voltage is applied, the two surfaceselectrostatically clamp together and rotation is transmitted from aninput stage to an output stage.

The method of the first concept, where a first surface is coupled toelectrical ground and where a second surface is coupled to an electricalpower source via a brush or a slip ring and where the second surface issupported by a pin structure with or without an axial spring. When novoltage is applied, the two surfaces can rotate relative to each otherbut when a voltage is applied, the two surfaces electrostatically clamptogether and rotation is transmitted from an input stage to an outputstage.

A second concept of a two speed transmission system using a first andsecond electrolaminate disc clutch and where the first disc clutch isassociated with one or more gear stages and where the second clutch isassociated with an output stage.

The two speed transmission system of the second concept, where theoutput of the device can be switched between a high speed low torqueoperation and a low speed high torque operation.

A third concept of a method of coupling an input stage to an outputstage by utilizing two discs and a band which traverses over the sidesurfaces of the two discs and where the band may be electrostaticallyclamped to the discs when a voltage is applied across the band and thetwo discs. When clamped, the input rotation is imparted to the outputstage which also begins to rotate. When the voltage is turned off, norotation is imparted to the output stage.

A fourth concept of a device that couples an input stage to an outputstage by utilizing a first (input) and a second (output) shafts andwhere a spring loosely couples to first or input shaft and tightlycouples to the second or output shaft; and where the spring has a tailcoupled to an electrolaminate surface such that when a voltage isapplied to the electrolaminate surface, it clamps to input shaft andimparts the rotation of the input to the output.

A fifth concept of a device which includes: (a) An input shaft coupledto an electrolaminate sheet; (b) An output shaft coupled rigidly to aspring positioned over the input shaft, the spring having a tab thatfits in a groove within a spring capture ring; (c) A spring capture ringalso positioned over the input shaft; and (d) A drum connected toelectrical ground positioned between the electrolaminate sheet and aspring capture ring; the drum being coupled rigidly to the springcapture ring; all in such a manner that when a voltage is applied to theelectrolaminate sheet, it clamps to the drum and imparts the rotation ofthe input to the drum, which then causes the spring capture ring torotate, which then subsequently causes the spring to rotate and clampdown on the input shaft, thus imparting rotation to the final output ofthe device.

A sixth concept of a method of utilizing two wrap-spring devices asdescribed as either the fourth concept or the fifth concept above on acommon shaft in order to transmit torque bi-directionally from an inputto an output.

X. CONCLUSION

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other embodiments may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anexemplary embodiment may include elements that are not illustrated inthe Figures.

Additionally, while various aspects and embodiments have been disclosedherein, other aspects and embodiments will be apparent to those skilledin the art. The various aspects and embodiments disclosed herein are forpurposes of illustration and are not intended to be limiting, with thetrue scope and spirit being indicated by the following claims. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the spirit or scope of the subject matter presentedherein. It will be readily understood that the aspects of the presentdisclosure, as generally described herein, and illustrated in thefigures, can be arranged, substituted, combined, separated, and designedin a wide variety of different configurations, all of which arecontemplated herein.

What is claimed is:
 1. A device for controlling transmission of torque,comprising: a first stage; a second stage; an electrolaminate clutchcomprising a first portion and a second portion, wherein the firstportion of the electrolaminate clutch is coupled to the first stage, andwherein the second portion of the electrolaminate clutch is looselycoupled to the second stage such that the first and second portions ofthe electrolaminate clutch can align together; and an electrical circuitelectrically connected to the first and second portions of theelectrolaminate clutch, wherein (i) when the electrical circuit appliesa voltage between the two portions, the two portions areelectrostatically clamped together such that torque is transmittedbetween the first and second stages and (ii) when the electrical circuitdoes not apply the voltage, torque is not transmitted between the firstand second stages.
 2. The device of claim 1, wherein the voltage appliedby the electrical circuit brings the second portion of theelectrolaminate clutch into alignment with the first portion of theelectrolaminate clutch.
 3. The device of claim 1, wherein the firststage is an input stage and the second stage is an output stage.
 4. Thedevice of claim 3, wherein the input stage comprises a motor.
 5. Thedevice of claim 3, wherein the output stage comprises a gearbox.
 6. Thedevice of claim 1, wherein the second portion of the electrolaminateclutch is loosely coupled to the second stage via a support member thatcan move relative to the second stage within a certain range.
 7. Thedevice of claim 6, wherein the support member is coupled to the secondstage via at least one pin that fits into an oversized hole in thesupport member.
 8. The device of claim 6, wherein the support membercomprises a larger disc and a smaller disc arranged concentricallytogether, wherein the second portion of the electrolaminate clutch isrigidly coupled to the smaller disc.
 9. The device of claim 8, whereinthe second portion of the electrolaminate clutch is flexible and iswider than the smaller disc.
 10. The device of claim 1, wherein at leastone of the first and second portions of the electrolaminate clutch isflexible.
 11. The device of claim 1, wherein at least one of the firstand second portions of the electrolaminate clutch has a thickness of0.09 inches or less.
 12. The device of claim 1, wherein each of thefirst and second portions of the electrolaminate clutch is flexible andcomprises a respective substrate, a respective conductive layer, and arespective dielectric layer, with the respective dielectric layers ofthe two portions facing each other.
 13. The device of claim 1, whereinthe first portion of the electrolaminate clutch is rigid and comprises ametal surface, and wherein the second portion of the electrolaminateclutch comprises a substrate, a conductive layer disposed on thesubstrate, and a dielectric layer disposed on the conductive layer withthe dielectric layer facing the first portion of the electrolaminateclutch.
 14. The device of claim 1, wherein the first portion of theelectrolaminate clutch comprises a first disk and the second portion ofthe electrolaminate clutch comprises a second disk.
 15. The device ofclaim 1, wherein the first portion of the electrolaminate clutchcomprises a first drum and the second portion of the electrolaminateclutch comprises a second drum.
 16. A method, comprising: controllingtransmission of torque between a first stage and a second stage using anelectrolaminate clutch comprising a first portion and a second portion,wherein the first portion is coupled to the first stage and the secondportion is loosely coupled to the second stage such that the first andsecond portions of the electrolaminate clutch can align together,wherein the controlling comprises: when a voltage is applied between thetwo portions of the electrolaminate clutch, the two portions areelectrostatically clamped together such that torque is transmittedbetween the first and second stages; and when the voltage is notapplied, torque is not transmitted between the first and second stages.17. The method of claim 16, wherein the voltage is applied by anelectrical circuit electrically connected to the first and secondportions of the electrolaminate clutch.
 18. The method of claim 16,wherein the voltage brings the second portion of the electrolaminateclutch into alignment with the first portion of the electrolaminateclutch.
 19. The method of claim 18, wherein the second portion of theelectrolaminate clutch is loosely coupled to the second stage via asupport member that can move relative to the second stage within acertain range, and wherein the voltage brings the second portion of theelectrolaminate clutch into alignment with the first portion of theelectrolaminate clutch by causing the support member to move relative tothe second stage.
 20. The method of claim 16, wherein at least thesecond portion of the electrolaminate clutch is flexible, wherein thevoltage causes the second portion of the electrolaminate clutch toconform to a shape of the first portion of the electrolaminate clutch.